Multiple stage hydrodesulfurization process with extended downstream catalyst life

Abstract

A multiple stage process for hydrodesulfurizing a residual oil while passing the oil downwardly through a plurality of stages in series with an interstage flashing step. After the catalyst in the downstream stage is deactivated by coke deposition, fresh feed oil is passed directly to the deactivated catalyst to obtain an extended life in the downstream catalyst.

We claim: 
     
       1. A process for hydrodesulfurization of residual feed oil comprising passing said oil and hydrogen downwardly through both first and second fixed bed catalytic hydrodesulfurization zones in series at a temperature of 600° and 900° F. and a hydrogen pressure of 500 to 5,000 psi, the catalyst in said zones comprising supported Group VI-B and Group VIII metals, flashing contaminant gases including hydrogen sulfide and ammonia from the oil flowing between said first and second zones, increasing the temperature in said zones to compensate for catalyst activity loss with increasing catalyst age, teminating said flow of said feed oil to said first zone when said second stage catalyst becomes substantially deactivated, and then directly charging said feed oil downwardly through said second zone thereby extending the operable life of said substantially deactivated second stage catalyst. 
     
     
       2. The process of claim 1 wherein said first zone catalyst becomes deactivated due to metals deposits on the catalyst and said first zone catalyst is being renewed while said residual feed oil is being charged through said second zone. 
     
     
       3. The process of claim 1 wherein the charging of said feed oil directly to the second zone reduces the coke level on the catalyst in said second zone.